1. Field of the Invention
The present invention relates to a heat exchanger, and more particularly, to a heat exchanger fin structure.
2. Description of the Related Art
A fin tube type heat exchanger functioning as an evaporator or condenser in an air conditioner or a refrigerator includes a plurality of heat exchange tubes arranged in parallel with each other in a plurality of rows and a plurality of plate-shaped fins spaced by an interval for conducting an air flow and arranged in parallel with each other perpendicular to the heat exchange tubes. The fins have a plurality of throughholes through which the heat exchange tubes are passed. A coolant flowing through the heat exchange tubes exchanges heat with air forcedly blown by an air blower transversely with respect to the longitudinal direction of the heat exchange tube, that is along the plate surface of the fin.
FIG. 5 is a plan view partially showing a conventional fin for use in a heat exchanger, and FIG. 6 is a partially sectional view taken along line II--II of FIG. 5. As can be seen from FIGS. 5 and 6, a plate-shaped fin 71 includes a plurality of throughholes 75 for passage of heat exchange tubes for transferring a coolant and a plurality of slit protuberance portions 77 and 79 protruding from a fin base 73 defining slits extending transversely with respect to the air flowing direction of the fin base 73. These slit protuberance portions 77 and 79 protrude alternately from both plate surfaces along the air flowing direction. Accordingly, the flow of the air flowing along the plate surface curves up and down with respect to the plate surface of the fin base 73 and the air exchanges heat with the coolant in the heat exchange tubes as shown in FIG. 6.
The conventional fin 71 of FIG. 5 includes three fin sections 81, 83 and 85 in which three heat exchange tube rows transversely arranged in parallel with respect to the air flowing direction are formed, respectively. An equal number of the slit protuberance portions 77 and 79 are formed in each of the fin sections 81, 83 and 85.
By the way, in the case of the fin 71 for use in the heat exchanger, since the difference in temperature between the air and the coolant in the upstream fin section 81 is large, the amount of heat exchange is comparatively large, while since the difference in temperature between the air and the coolant in the downstream fin section 85 is small, the amount of heat exchange is comparatively small. The deviation of the heat exchange amount lowers a heat exchange efficiency of each fin or the whole heat exchanger.
For example, assuming that the heat exchanger is used as a condenser of an air conditioner and has the conventional fin 71 in which the number of slit protuberance portions 77 and 79 is uniform, when the temperature of the heat exchange tube and the fin is about 70.degree. C., the temperature of the outer air before passing through the heat exchanger is about 30.degree. C. and the humidity is about 75%, it has been proved experimentally that approximate 50-70% of the total heat exchange amount is accomplished in the first fin section 81, approximate 30% thereof is accomplished in the second fin section 83 and approximate 10% thereof is accomplished in the third fin section 85.
In particular, when a heat exchanger is used as an outdoor heat exchanger during heating operation in an air conditioner operating as a cooler and heater in combination, there is a high possibility that a layer of frost will be formed on the fin section 81 of the entrance side having a large amount of heat exchange due to the low ambient temperature and the evaporation latent heat of the coolant, compared to that of the fin section 85 of the exit side having a small amount of heat exchange. The frost stops up the slit protuberance portions and hinders air from flowing, to thereby adversely affect the heat exchange at the fin sections 83 and 85. Such a problem can occur likewise when a heat exchanger is used as an evaporator for use in a refrigerator.